1. Field of the Invention
The present invention relates generally to cookware and, more particularly, to induction cookware having an inductor layer with a predetermined Curie temperature. Still more particularly, one embodiment of the present invention relates to food warming apparatus, trays and/or chafing dishes containing an inductor portion or layer with a Curie temperature approaching the boiling point of water. The present invention is also directed generally to induction cookware apparatus for cooking at a predetermined temperature range such as, for example, a popcorn maker, waffle maker, fondue pot, rice cooker and the like.
2. Description of Related Art
Induction cookware is generally well-known in the art for use on an induction cooking stove. This cookware has a ferromagnetic inductor bottom generally of a carbon steel or ferritic stainless steel and the induction stove or range has induction coils to cause heating in the inductor. Temperature is regulated much like a conventional natural gas or electric range by regulating the electric power input of the induction cooking unit.
In the food service industry, it is well-known to use warming trays, tables or chafing dishes to keep the food at an acceptably high temperature prior to and during serving. These food warming utensils, hereinafter sometimes referred to as “chafing dishes”, commonly employ a water-containing vessel situated beneath the food holding vessel. A heat source in the form of an electrical heater, gas flame, or sterno or the like is positioned beneath the water-containing vessel to heat the water. The heated water then ideally supplies a sufficient amount of heat to the food contained in the upper vessel during the food serving period so as to enhance the dining experience.
It is, however, common that too little heat may be supplied to the water-containing vessel, in which case the food is not heated properly. On the other hand, if too much heat is supplied, the water in the lower vessel will boil, causing the water to dissipate, which requires periodic replenishment. The boiling water also generates steam. The steam rises and condenses in the upper food-containing vessel, causing the food to become soggy and otherwise less attractive and/or less palatable.
Chafing dishes and similar prior art devices which operate at a single optimal temperature are typically heated by contact resistance elements. These are controlled by contact thermostats and are equipped with over-temperature switches. An example of a resistance heated chafing dish is disclosed in U.S. Pat. No. 5,597,500 to Hasenfratz et al., which is incorporated by reference herein. Listed below are some distinct advantages which the self-regulating induction concept offers over both resistance and traditional induction heat:
(1) Induction is a faster method of heating a vessel than resistance. Resistance must conduct energy across a mechanical attachment. Induction preferably uses the vessel as the heating element.
(2) Induction is a more evenly distributed heat source. Since the magnetic flux is as wide as the drive coil, energy is evenly dispersed. Resistance heat must often be buffered with a thick conductor, making it slow and inefficient.
(3) Because the induction drive heats only the cooking vessel, it is more energy efficient than resistance.
(4) Resistance elements must be mechanically attached to the vessel, making them difficult to remove for cleaning. The induction vessel can be held in the appliance by conventional means, which can make it easily removable for cleaning.
(5) Self-regulating induction allows the construction of the appliance to be simple and cost effective. Temperature control is inherent to the alloy of the inductor. Hence, there is no need for costly thermal feedback controls and no possibility of overheating or underheating. The induction drive is less complicated and less costly, more compact and easier to use with the appliance than traditional heating units.
A commercial-style flat griddle having a plurality of griddle plates of different Curie temperatures is disclosed in U.S. Pat. No. 5,134,265 and a popcorn popper having an induction heated kettle is disclosed in U.S. Pat. No. 5,928,550, both of which are incorporated by reference herein. Induction heating cookware is disclosed in French Patent No. 2,527,916 wherein several pots and pans are provided with a magnetic stainless steel plate at the bottom which are said to have different Curie temperatures to produce different cooking temperatures for each utensil.
The present invention solves the problems encountered in the prior art by providing a vessel for cooking at a specified temperature wherein the bottom or a portion of the bottom of the vessel is made from a ferromagnetic Ni—Fe alloy material having a well-defined Curie temperature in the narrow temperature range desired for the desired cooking or heating application required. The vessel having a bottom portion of a specific Ni—Fe alloy composition for providing a Curie temperature in a desired range is combined with an induction heating unit to form a self-contained, unitary appliance for cooking or heating a particular food or foods such as, for example, a self-contained popcorn popper, a waffle iron, a fondue pot, a rice cooker, deep frier, a chafing dish or like appliances.